Power supply apparatus and control circuit therefor

ABSTRACT

A selector sets respective phases of pulse driving signals in reverse when a proportion signal or integration signal does not exceed a threshold. Shifting the respective phases of the pulse driving signals from each other lowers the ripple voltage. When the load current increases drastically, the output voltage Vo tends to decrease remarkably because of the shortage of capacity in the power supply. In this case, when the proportion signal or integration signal exceeds its corresponding threshold, a phase control unit causes the pulse driving signals to synchronize their phases, i.e., the selector supplies the same ramp wave to the comparators, so that respective output voltages supplied from the DC voltage converter circuits attain the same phase, thereby restraining the output voltage supplied to the load from decreasing remarkably.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power supply apparatus comprising aplurality of power converter circuits connected in parallel, and acontrol circuit therefor.

2. Related Background Art

As a conventional switching power supply apparatus, one disclosed inJapanese Patent Application Laid-Open No. HEI 7-203672 has been known,for example. In a power supply apparatus employing a PWM control schemewhich carries out voltage control for causing an actual output voltagevalue to coincide with a target voltage value, the switching powersupply apparatus disclosed in the reference uses different outputvoltage controlling parameters for a start up period to the targetvoltage value and for a steady state after the target voltage value isattained, thereby providing a power supply apparatus which is excellentin start up period and steady-state characteristics.

As the processing in microprocessors and digital signal processing (DSP)circuits mounted in personal computers, communication devices, and thelike has become faster, the power consumption in such a device has beenlowered. As a result, the voltage applied to integrated circuits(operating voltage) has become lower, thus requiring precision powermanagement in conformity to operating states.

SUMMARY OF THE INVENTION

In a control system of a switching power supply, however, the outputresponse and the stability of the control system are contradictory toeach other. When the gain of the control system is enhanced in order toreduce the response time, the output voltage is more likely tooscillate. When the gain is lowered, by contrast, the responsedeteriorates, though the stability of the control system can be secured.For example, when a processor acting as a load shifts from a so-calledsleep mode to an active mode, so that the load current increasesdrastically, the output voltage cannot follow the drastic increase inload current, whereby the output voltage may be in a lowering. When theload current decreases drastically, by contrast, the output voltage maybecome in over voltage. If a plurality of capacitors are used in theoutput stage in order to prevent such a phenomenon from occurring, theapparatus will increase its size.

In view of such problems, it is an object of the present invention toprovide a power supply apparatus which favorably follows the loadcurrent without losing the stability of the control system and isexcellent in the stability of output voltage, and a control apparatustherefor.

For overcoming the above-mentioned problems, the present inventionprovides a control apparatus for a power supply apparatus comprising aplurality of power converter circuits connected in parallel; each powerconverter circuit comprising a switch circuit for forming a pulse-likewaveform by switching an inputted power according to a pulse drivingsignal, and a smoothing circuit for converting the pulse-like waveforminto a direct current and outputting the direct current; the controlapparatus comprising a feedback control unit for changing, according toa magnitude of an arithmetic value summing a proportion signal inproportion to a deviation of an output voltage of the power convertercircuit from a reference voltage and an integration signal integratingthe deviation, a duty ratio of the pulse driving signals applied toswitching devices of the power converter circuits; and a phase controlunit for causing the pulse driving signals to synchronize phases thereofwhen the proportion signal or integration signal exceeds a thresholdthereof.

This control apparatus applies a pulse driving signal to a switchingdevice of a power converter circuit, whereby an output voltage occursbetween output terminals according to the duty ratio of the pulsedriving signal. Since a plurality of such power converter circuits areconnected in parallel with the load, each power converter circuitsupplies a DC voltage to the load.

Here, the duty ratio is adjusted by using the proportion control andintegration control in the feedback control unit. Namely, the feedbackcontrol unit changes duty ratios of pulse driving signals applied toswitching devices of the power converter circuits according to themagnitude of an arithmetic value summing a proportion signal inproportion to a deviation of an output voltage of the power convertercircuit from a reference voltage and an integration signal integratingthe deviation.

Therefore, so-called PI control is executed. Here, a differential valueof the deviation may be used as an additional arithmetic value, wherebyso-called PID control is executed.

Shifting the respective phases of the pulse driving signals from eachother can reduce the ripple voltage component in the voltage suppliedfrom such a power supply apparatus to the load.

When the load current increases drastically, the decrease of outputvoltage tends to become remarkable unless the control system response tothe drastic increase. Therefore, in the control apparatus of the presentinvention, the phase control unit causes the pulse driving signals tosynchronize their phases when the proportion signal or integrationsignal exceeds a threshold thereof. The power converter circuitsoperating in synchronization with each other restrain the output voltagesupplied to the load from decreasing remarkably.

Therefore, this control apparatus improves the responsibility to theload current, since the phase control unit carries out phase adjustmentif the load increases, even when the gain of PI control unit is set soas to fully secure the stability of the control system.

The threshold to be compared with the proportion signal or integrationsignal may be changed by threshold changing means according to operationmode. This can adjust the switching power supply start up time and theoutput response, for example.

Such a power supply apparatus comprises the control circuit and aplurality of the power converter circuits connected in parallel andcontrolled by the control circuit, thus becoming a power supplyapparatus which can favorably response the load current and is excellentin the stability of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a power supply apparatus comprising aplurality of switching power supplies 1 connected in parallel.

FIG. 2 is a block diagram showing the inner configuration of acontroller IC 7.

FIG. 3A is a timing chart of the current I (load current lo and detectedcurrents I_(L1), I_(L2)) in the circuit shown in FIG. 2.

FIG. 3B is a timing chart of output voltage Vo in the circuit shown inFIG. 2.

FIG. 3C is a timing chart of pulse driving signal D₂ in the circuitshown in FIG. 2.

FIG. 3D is a timing chart of pulse driving signal D₁ in the circuitshown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following, the control apparatus for switching power supplyapparatus and the switching power supply apparatus in accordance withembodiments will be explained with reference to the drawings.

FIG. 1 is a block diagram of a power supply apparatus comprising aplurality of switching power supplies 1 arranged in parallel.

Each switching power supply 1 includes a pair of input terminals IT1,IT2 to which a DC voltage Vi is applied, and a pair of output terminalsOT1, OT2 which are connected to a load L. One of the two input terminalsIT1, IT2 is grounded, whereas the other is connected to one ofpotentials of a DC voltage source P. The load L is connected between thetwo output terminals OT1, OT2. These input and output terminalsconstitute a four-terminal circuit.

The load L is a destination to which an output voltage Vo output fromthe switching power supply 1 is fed. Examples of the load L include CPU(Central Processing Unit) and MPU (Micro Processing Unit) used in PCterminals and the like. Such CPU and MPU have a power-saving mode, andare characterized in that load fluctuations drastically increase whenshifting from the power-saving mode to a normal mode.

The switching power supply 1 is a noninsulated step-down DC/DC converterwhich converts a higher DC input voltage Vi into a lower output voltageVo. A controller IC (control unit) 7 for carrying out voltage controlgenerates pulse driving signals (PWM signals) D (D₁, D₂) according tothe output voltage Vo converted into a digital value by an A/D converter6, and applies the PWM signals D to switching devices 2, 3 of theircorresponding DC voltage converter circuits (power converter circuits).

The switching device 2 has one end connected to an input terminal, andthe other end connected to a coil 4. The switching device 3 has one endconnected to the switching device 2, and the other end connected to theground. The conducting/non-conducting of the switching devices 2, 3 isregulated according to inputs of the PWM signals D. Fed into theswitching device 3 is a pulse driving signal complementary to the PWMsignal D inputted to the switching device 2, whereby the switchingdevice 3 is non-conducted and conducted when the switching device 2 isshort-circuited and opened, respectively. As the switching devices 2, 3,bipolar transistors and field-effect transistors can be employed.

The coil 4 is connected in series between the output terminal OT1 andthe junction between the switching devices 2, 3, whereas a capacitor 5is connected between the output terminals. The coil 4 and capacitor 5constitute a smoothing circuit, which is disposed downstream theswitching devices 2, 3 and smoothes the pulse voltage generated byON/OFF of the switching devices 2, 3, thereby converting it into a DCvoltage.

The output voltage Vo becomes higher as the pulse width of PWM signal D,i.e., the time during which the switching device 2 is ON (duty ratio),increases.

The smoothing circuit is provided with a detecting device (detectingunit) dt for detecting the current (=output current) flowing through thecircuit. The detecting device dt is a hole sensor, for example. Thedetected current I_(L) (of which respective detected currents of theswitching power supplies will be referred to as I_(L1), I_(L2)) andoutput voltage Vo are converted into digital values by the A/D converter6, and thus obtained digital values are fed. into the controller IC(control unit) 7. The controller IC can be realized by an analog/digitalmixed signal IC.

Namely, according to the digital input information I_(L) (I_(L1),I_(L2)) and Vo, the controller IC 7 generates the PWM signals D (D₁,D₂).

FIG. 2 is a block diagram showing the inner configuration of thecontroller IC 7.

The controller IC 7 comprises an adder 7 a for outputting a deviation ΔV(=Vr−Vo) of the output voltage Vo from the reference voltage Vr, a PIcontrol unit 7 b for receiving the deviation ΔV output from the adder 7a, a current compensator 7 c for receiving a deviation-dependentarithmetic value CS output from the PI control unit 7 b together withthe current I_(L1), a current compensator 7 d for receiving thearithmetic value CS together with the current I_(L2), a comparator 7 efor receiving a deviation-dependent arithmetic value C1 output from thecurrent compensator 7 c and a first ramp wave (ramp1), and a comparator7 f for receiving a deviation-dependent arithmetic value C2 output fromthe current compensator 7 d and the first or second ramp wave (ramp1,ramp2).

The controller IC 7 also comprises a selector 7 g which switches betweenthe ramp waves to be fed into the comparator 7 f in response to theoutput of the PI control unit 7 b. The phase of the first ramp wave(ramp1) shifts from that of the second ramp wave (ramp2) by 180° (i.e.,their phases are in reverse).

The PI control unit 7 b is a major part of feedback control, whichsubjects the deviation ΔV to the following processing and outputs thusprocessed deviation to the current compensators 7 c, 7 d.

The feedback control is control in which, in order for a targetreference voltage Vr and an output voltage Vo of the system to coincidewith each other, the deviation ΔV (=Vr−Vo) of the output voltage Vo fromthe reference voltage Vr is subjected to appropriate processing and thenis fed back to an input. Known as control schemes in the feedbackcontrol are P (proportion) control, I (integration) control, D(differentiation) control, and so forth.

For the P control, the PI control unit 7 b comprises an amplifier P1 formultiplying the deviation ΔV by a constant of proportion kp andoutputting the result. The resulting arithmetic value kp×ΔV becomesgreater as the output voltage Vo is lower, i.e., the deviation ΔV isgreater. As the deviation ΔV is greater, the time interval given by thearithmetic value kp×ΔV and the ramp wave becomes longer, i.e., the dutyratio of the pulse driving signal increases, whereby the output voltageVo becomes higher. In other words, when the output voltage Vo decreasesalong with the increase in load current, the output voltage Vo tends toincrease under the P control and thus is restrained from decreasing.

For the I control, the PI control unit 7 b further comprises anintegrator I1 for integrating (accumulating) the deviation ΔV, and anamplifier I2 for multiplying the integrated deviation (∫ΔVdt) by aconstant of proportion ki and outputting the resulting arithmetic value(ki×∫Δvdt).

The I control can improve disturbance eliminating performances in lowfrequency bands, and thus can reduce steady-state deviations whencombined with the P control.

The D control is control setting a term in proportion to thedifferential value of the deviation ΔV, and has been known as a controlscheme which improves both the response speed and the stability of thesystem when combined with the PI control so as to effect PID control. Ageneral expression of the PID control is given byCS=Kp×ΔV+Ki×∫ΔVdt+Kd×dΔV|dtwhere Kp is a feedback gain (proportion element), Ki is a feedback gain(integration element), and Kd is a feedback gain (differentiationelement).

Since this example illustrates the PI control, the differential term inthe expression of CS will be neglected. Namely, the PI control unit 7 bcomprises an adder A1 for adding the arithmetic value (Kp×ΔV) of Pcontrol and the arithmetic value (Ki×∫ΔVdt) of I control. The arithmeticvalue CS output from the adder is fed into the current compensators 7 c,7 d. As mentioned above, the response speed becomes faster as thefeedback gain Kp is made greater, whereas steady-state deviations becomesmaller as the feedback gain Ki is made greater. When the feedback gainsare too large, however, the control system becomes unstable, and theoutput voltage oscillates. Therefore, the feedback gains are set suchthat the stability of the system can fully be secured.

The current compensators 7 c, 7 d are subtractors, for example, andenhance the accuracy of feedback control according to actually measuredmagnitudes of output currents I_(L1), I_(L2).

The arithmetic value C1 (or CS) output from the current compensator 7 cand the first ramp wave (ramp1) are fed into the comparator 7 e. Thecomparator 7 e outputs H and L levels when the arithmetic value C1 isgreater than the first ramp wave (ramp1) and not, respectively. Namely,the duty ratio of the pulse driving signal D₁ generated by this levelfluctuation is in proportion to the arithmetic value C1 (or CS).

The arithmetic value C2 (or CS) output from the current compensator 7 dand the first or second ramp wave (ramp1, ramp2) are fed into thecomparator 7 f. The comparator 7 f outputs H and L levels when thearithmetic value C2 is greater than the ramp wave and not, respectively.Namely, the duty ratio of the pulse driving signal D₂ generated by thislevel fluctuation is in proportion to the arithmetic value C2 (or CS).

More specifically, the feedback control unit constituted by the elements7 a, 7 b, 7 e, 7 f changes duty ratios of the pulse driving signals D₁,D₂ applied to the switching devices 2, 3 of the DC voltage convertercircuits according to the magnitude of arithmetic value CS summing theproportion signal in proportion to the deviation ΔV of the outputvoltage Vo between the output terminals from the reference voltage Vrand the integration signal integrating the deviation ΔV.

When the pulse driving signals D₁, D₂ are applied to the switchingdevices 2, 3 of the DC voltage converter circuits, the output voltage Vooccurs between the output terminals according to the duty ratios of thepulse driving signals D₁, D₂. Since a plurality of such DC voltageconverter circuits are connected in parallel with the load L, each DCvoltage converter circuit supplies a DC voltage to the load L.

Here, the first or second ramp wave is selected by the selector 7 g. ThePI control unit 7 b determines a selecting criterion for the selector 7g.

Namely, the PI control unit 7 b comprises comparators J1, J2 fordetermining whether or not the proportion signal (kp×ΔV) and integrationsignal (ki×∫ΔVdt) are greater than their thresholds PMAX and IMAX,respectively; and an OR circuit J3 which outputs an H level when theresult of determination of any of the comparators J1, J2 is greater thanits corresponding threshold. The selector 7 g selectively feeds thefirst ramp wave (ramp1) and second ramp wave (ramp2) into the comparator7 f when the H and L levels are output from the OR circuit,respectively.

Namely, the determining sections J1, J2, J3 and selector 7 g constitutea phase control unit which causes the pulse driving signals D₁, D₂ tosynchronize their phases when any of the signal (kp×ΔV) and integrationsignal (ki×∫ΔVdt) is greater than its corresponding threshold PMAX,IMAX.

When the proportion signal or integration signal does not exceed itscorresponding threshold, the selector 7 g sets the respective phases ofthe pulse driving signals D₁, D₂ in reverse to each other. Shifting thephases of the pulse driving signals from each other is also advantageousin that the ripple voltage is lowered in the voltage supplied to theload L.

When the load current increases drastically, the feedback gain set bythe PI control unit may fail to follow the drastic change, therebyremarkably lowering the output voltage Vo. In this case, the proportionsignal or integration signal of the phase control unit exceeds itscorresponding threshold, whereby the phases of the pulse driving signalscoincide with each other. Namely, the selector 7 g supplies the sameramp wave (ramp1) to the comparators 7 e, 7 f, so that the respectiveoutput voltages supplied from the DC voltage converter circuits have thesame phase, thereby restraining the output voltage supplied to the loadL from decreasing remarkably.

As explained in the foregoing, the controller IC 7 and the power supplyapparatus regulated thereby improve the followability to the loadcurrent without making the control system unstable, thus achieving anexcellent stability in output voltage.

The respective thresholds to be compared with the proportion signal andintegration signal can be made variable in response to operating states.An example of threshold changing means is a switch or the like whichchanges the thresholds in response to an input from a user. In otherwords, the thresholds are variable. This can adjust the start up timefor the power supply apparatus, for example. From the instant at whichthe DC voltage Vi is applied upon connection with the DC voltage sourceP until the output voltage attains a steady state (the deviation ΔVbecomes substantially zero), the DC voltage converter circuits operatein synchronization with each other if the thresholds are set lower,whereby the starting time can be made shorter. By contrast, the startingtime can be made longer by increasing the thresholds. Theabove-mentioned control apparatus can also be employed in AC/DCconverters whose input voltages are AC signals.

FIG. 3A is a timing chart of the current I (load current Io and detectedcurrents I_(L1), I_(L2)), FIG. 3B is a timing chart of output voltageVo, FIG. 3C is a timing chart of pulse driving signal D₂, and FIG. 3D isa timing chart of pulse driving signal D₁. in the circuit shown in FIG.2.

As mentioned above, along with the drastic increase in load current Ioafter a time t1, the output voltage Vo decreases. In this case, thepulse driving signals D₁, D₂, which have been in reverse phases so far,attain the same phase, whereby the output voltage is seen to increasegradually.

As explained in the foregoing, the control apparatus in accordance withthe above-mentioned embodiment is a control apparatus for a power supplyapparatus comprising a plurality of power converter circuits connectedin parallel; each power converter circuit comprising a switch circuit(2, 3) for forming a pulse-like waveform by switching an inputted poweraccording to a PWM signal D, and a smoothing circuit (4, 5) forconverting the pulse-like waveform into a direct current and outputtingthe direct current; the control apparatus comprising a feedback controlunit (7 a, 7 b, 7 e, 7 f) for changing, according to the magnitude of anarithmetic value CS summing a proportion signal (kp×ΔV) in proportion toa deviation (ΔV) of an output voltage Vo of the power converter circuitfrom a reference voltage Vr and an integration signal (ki×∫ΔVdt)integrating the deviation ΔV, a duty ratio of the PWM signals D appliedto switching devices 2, 3 of the power converter circuits; and a phasecontrol unit (J1, J2, J3, 7 g) for causing the PWM signals D tosynchronize phases thereof when the proportion signal (kp×ΔV) orintegration signal (ki×∫ΔVdt) exceeds its corresponding threshold PMAX,IMAX. The phase matching effected by the phase control units allows thepower converter circuits to operate in synchronization, whereby theoutput voltage supplied to the load L can be restrained from decreasingremarkably.

The power supply apparatus regulated by the control apparatus of thepresent invention favorably follows the load current without making thecontrol system unstable, and thus is excellent in the stability ofoutput voltage.

1. A control circuit for a power supply apparatus comprising a pluralityof power converter circuits connected in parallel; each power convertercircuit comprising a switch circuit for forming a pulse-like waveform byswitching an inputted power according to a pulse driving signal, and asmoothing circuit for converting the pulse-like waveform into a directcurrent and outputting the direct current; the control circuitcomprising a feedback control unit for changing, according to amagnitude of an arithmetic value summing a proportion signal inproportion to a deviation of an output voltage of the power convertercircuit from a reference voltage and an integration signal integratingthe deviation, a duty ratio of the pulse driving signals applied toswitching devices of the power converter circuits; and a phase controlunit for causing the pulse driving signals to synchronize phases thereofwhen the proportion signal or integration signal exceeds a thresholdthereof.
 2. A control circuit according to claim 1, wherein saidthreshold is variable.
 3. A power supply apparatus comprising thecontrol apparatus according to claim 1, wherein the plurality of powerconverter circuits are connected in parallel, and wherein the powerconverter circuits are controlled by the control circuit.